1. Field of the Invention
The present invention relates generally to pressure relief systems and, more particularly, to a rupture disc for use in relieving pressure differentials in low-pressure industrial applications and the like.
2. Discussion of the Prior Art
It is conventional to employ a rupture disc as a safety pressure relief apparatus in industrial applications for venting excess pressure differentials within pressurized components or equipment in order to prevent damage to the equipment.
Typically, the construction of a rupture disc includes a unitary disc having a circular central dome region and an outer annular flange. The dome presents a concavo-convex shape corresponding to the shape of the relief passage within which the disc is positioned, and the disc is oriented with the concave surface of the dome in contact with the pressure to be relieved. This construction is referred to as a forward-acting device.
A line of weakness is provided in the disc which substantially circumscribes the dome except for a small portion of the circumference of the central dome region which serves as a hinge when the dome region breaks free of the annular flange during rupture. The line of weakness typically includes a scored line formed in one surface of the disc by any known method.
Conventional discs may be formed of any of a number of different materials, and are operable over a broad range of pressures. However, because of the characteristics of these conventional devices, the equipment should only be operated at pressures up to 80% of the pressure at which the disc is designed to burst in order to avoid premature rupture of the disc. In addition, these discs are not presently constructed to reliably vent low pressures. e.g. in the range of 10-80 psi. for a two inch diameter disc.
In contrast to these forward-acting discs, assemblies of the reverse-acting type are also known, and are typically capable of handling normal operating pressures up to 90% of the rated pressure of the disc. These assemblies typically include a disc having a central dome region of concavo-convex shape, wherein the disc is positioned in the relief passage with the convex surface in contact with the positive pressure to be relieved.
In reverse-acting rupture discs, it is possible to employ a line of weakness around the dome region in order to control both the pressure at which rupture occurs and the manner in which the dome region tears to allow relief of the pressure. For example, it is known to provide lines of weakness across the dome region in order to cause the dome region to tear into quarters which are folded back under a relief pressure.
One concern with reverse-acting rupture discs of this type is that it is difficult to obtain a construction which is able to reliably vent low pressures, e.g. in the range of 10-80 psi. for a two inch diameter disc.
It is known to employ a knife blade assembly in a reverse-acting rupture disc assembly as a means for ensuring that the disc ruptures at low pressures when buckling of the disc occurs. In these systems, the knife blade is located downstream of the disc in the direction of travel of the positive pressure being relieved, adjacent the concave surface of the disc.
Because the blade must be disposed on a particular side of the disc, there are particular applications in which the blade assembly is exposed to corrosive environments which corrode the blade to the point of failure. In addition, the existence of a knife blade in a rupture disc assembly presents the potential for injury to installers and maintenance personnel, and is undesirable.